OrthoSAM is a new method that uses Segment Anything Model (SAM) to automatically identify and outline individual pebbles in high-resolution aerial images. OrthoSAM divides large photos into smaller sections that SAM can process effectively, and it improves the way to tell SAM where to look for objects. It uses a multi-resolution approach to handle different sizes, and it can be used to determine the distribution. Tests with computer-generated images and field data show that it is very precise.